Although myxoviruses and oncornaviruses are associated with different manifestations, they share properties which make the investigation of their structures amenable to similar experimental approaches. The glycoproteins and lipids on the surface of these virions determine many of these shared physical and biological properties. The objective of this proposal is to determine relationships between the biological activities of these virions and their chemical and physical structures. The approach presented here is based on the assumption that molecular requirements for at least some of their infectious and disease-producing capacities can be determined by modifying virions in specific ways by in vitro reactions and then correlating the remaining biological activities of these in vitro-modified particles with their chemical and physical properties. In order to do this, alterations in the carbohydrate moieties of the viral glycoproteins and in the viral lipids will be made using appropriate enzymes and other agents which induce small, specific chemical changes. Attempts will also be made to determine what is the smallest infectious subviral particle which can be obtained from oncornaviruses and from the influenza viruses. Finally, in vitro protein synthesis will be used to determine which of the influenza virion RNA segments are responsible for directing the synthesis of the virion proteins. It is proposed that experiments be carried out on the oncornaviruses and the myxoviruses at the same time so that comparisons can be made and so that enzyme preparations and technical procedures required for the investigation of both of these groups of viruses can be put to efficient use.